Linear compressor and control method thereof

ABSTRACT

A linear compressor having a core combined to one end of a piston to detect a position of the piston reciprocally moving up and down, and a bobbin having a first sensor coil and a second sensor coil that detect the position of the core. A controller determines the state of a load on the piston by measuring the time the core takes to exit and enter the bobbin from an inhale stroke through a compression stroke of the piston and control a position of the piston based on the measured state of the load. A method for controlling the operation of the linear compressor including timing the core driven by a piston through a stroke cycle, receiving the time and computing a load on the piston, outputting a piston position signal based on the load computed, and controlling a piston stroke according to the piston position signal, by varying the power driving the linear compressor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2003-46207, filed Jul. 8, 2003, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a linear compressor and a controlmethod thereof. A linear compressor is widely used to compress coolantin a freezing cycle such as in equipment like a refrigerator, freezer,etc. The linear compressor measures the magnitude of a stroke of apiston, and controls an operation of the piston by applying a current toa driving motor of the linear compressor based on an analysis of themeasured magnitude of the stroke.

2. Description of the Related Art

FIG. 1 is a cross-sectional view of a position detection sensor for apiston of a conventional linear compressor. As illustrated in FIG. 1,the position detection sensor comprises a bobbin 100, a sensor coil 101,a core support 102, and a core 103.

The bobbin 100 includes the sensor coil 101 inside, and the sensor coil101 is connected in series to a first sensor coil 101 a and a secondsensor coil 101 b each having the same inductance value, size, andnumber of turns. The core support 102 is made of non-magnetic materialand supports the core 103 and is combined to the piston (not shown).

As the core 103 combined to the piston of the compressor reciprocallymoves back and forth along an inner hole of the bobbin 100, apredetermined reactance is generated in the sensor coil 101 according toreciprocal movement of the piston.

FIG. 2 is a diagram of a conventional position detection circuit for thepiston of the conventional linear compressor. As illustrated in FIG. 2,two serial sensor coils 101 are connected in parallel with two serialdividing resistors Ra and Rb, and a triangle pulse is input as a powersource 105. A difference of voltages divided by the dividing resistorsRa and Rb is amplified by an amplifier 104 to detect a maximum outputvoltage according to the piston in which the core 103 moves back andforth starting from a center point between the first sensor coil 101 aand the second sensor coil 101 b. An analog signal processor 106receives an output pulse from the amplifier 104 and detects the positionof the piston through a predetermined signal process.

FIG. 3 illustrates an output pulse from the amplifier 104 in FIG. 2according to the reciprocal movement of the piston of the linearcompressor. As illustrated in FIG. 3, the output voltage from theamplifier (line “a”) has a linear output property for the reciprocalmovement of the piston. The position of the piston can be detected withthe output voltage because the output voltage is proportional to theposition of the piston.

However, the sensor circuit of the conventional linear compressor mayvary the angle of slope of the linear graph according to externalenvironmental conditions such as temperature and pressure. If the sensorcircuit of the conventional linear compressor follows the linearproperty represented by a small angle of the slope like a line “b” dueto the external environmental conditions, the piston controlledaccording to a steady operation when in a high cooling capacity maycollide with a valve of a cylinder.

The conventional linear compressor uses a control method for controllingthe reciprocal movement of the piston by determining a state of a loadon the linear compressor based on a measured temperature or a measureddriving current for a motor. The conventional control method ofdetermining the state of the load on the linear compressor may respondto a change of the load on the piston late. Additionally it is hard tomeasure the temperature and the driving current accurately in a linearcompressor, even if measuring points for the temperature and the drivingcurrent are properly selected.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide alinear compressor outputting cooling power actively and controlling astroke of a piston by determining state of a load on the pistonaccurately regardless of an external environment.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

The foregoing and/or other aspects of the present invention are achievedby providing a linear compressor having a core combined to one end of apiston to detect a position of the piston reciprocally moving up anddown, and a bobbin having a first sensor coil and a second sensor coildetecting the position of the core, comprising a controller determiningstate of a load of the piston by measuring an elapsed time for the coreto exit and enter the bobbin from an inhale stroke through a compressionstroke of the piston and controlling a position of the piston based onthe measured state of the load.

According to an aspect of the invention, the core has a length shorterthan one half of the length of the first sensor coil and the secondsensor coil in series.

According to an aspect of the invention, the controller increases a topclearance of the piston if the amount of time taken for the core to exitand enter the bobbin increases greatly over a predetermined criticaltime.

According to an aspect of the invention, the linear compressor includesa first branch including the first sensor coil and a predetermined firstdividing resistor connected in series, a second branch including thesecond sensor coil and a predetermined second dividing resistorconnected in series, a power source applied to the first branch and thesecond branch, and a voltage comparator with voltage inputs applied tothe first dividing resistor and the second dividing resistor.

According to an aspect of the invention, the voltage comparator hasvoltage inputs applied to the opposite terminals of each of the firstsensor coil and the second sensor coil.

According to an aspect of the invention, the controller determines thestate of the load on the piston on a basis of difference of time takenfor the piston to be positioned near the bottom dead center makingoutput of the voltage comparator zero (0) so as to control the positionof the piston.

According to an aspect of the invention, the controller determines thestate of the load on the piston on a basis of difference of time takenfor the piston to be positioned near the bottom dead center makingoutput of the voltage comparator zero (0), so as to control the positionof the piston.

According to another aspect of the present invention, the above andother aspects may be also achieved by providing a control method of alinear compressor having a core combined to one end of a piston todetect a position of the piston reciprocal moving up and down, and abobbin having a first sensor coil and a second sensor coil detecting theposition of the core, including measuring time taken for the core toexit and enter the bobbin from an inhale stroke through a compressionstroke of the piston; and controlling a position of the piston bydetermining state of a load on the piston on a basis of the time takenfor the core to exit and enter the bobbin.

According to an aspect of the invention, the control method of thelinear compressor further comprising forming length of the core to beshorter than a half of length of the first sensor coil and the secondsensor coil connected in series.

According to another aspect of the present invention, the above andother aspects may be achieved by providing the control method of thelinear compressor including increasing a top clearance of the piston ifthe time taken for the core to exit and enter the bobbin increasesgreatly than a predetermined critical time.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects and advantages of the present inventionwill become apparent and more readily appreciated from the followingdescription of the embodiments, taken in conjunction with the accompanydrawings of which:

FIG. 1 is a cross-sectional view of a position detection sensor for apiston of a conventional linear compressor;

FIG. 2 is a diagram of a position detection circuit for the piston ofthe conventional linear compressor;

FIG. 3 illustrates an output waveform from an amplifier in FIG. 2according to reciprocal movement of the piston of the linear compressor;

FIG. 4 is a cross-sectional view of a position detection sensor for apiston of a linear compressor according to an embodiment of the presentinvention;

FIG. 5 is a block diagram of a position detection circuit for the pistonof the linear compressor according to an embodiment of the presentinvention;

FIGS. 6A-6C and 7A-7C are input waveforms of a voltage comparatoraccording to reciprocal movement of the linear compressor;

FIG. 8 is a control block diagram of the linear compressor according toan embodiment of the present invention; and

FIG. 9 is an output waveform of the voltage comparator according to aposition of the piston of the linear compressor according to theembodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below to explain the presentinvention by referring to the figures.

FIG. 4 is a cross-sectional view of a position detection sensor for apiston of a linear compressor according to an embodiment of the presentinvention. As illustrated in FIG. 4, the position detection sensorcomprises a bobbin 1, a sensor coil 2, a core support 3, and a core 4.

The bobbin 1 includes a sensor coil 2 inside, and the sensor coil 2comprises a first sensor coil 2 a and a second sensor coil 2 b. Thefirst sensor coil 2 a and the second sensor coil 2 b have the sameinductance value, size, and number of turns and are connected in series.The core support 3 is made of non-magnetic material and supports thecore unit 4 and is combined to the piston (not shown).

The core unit 4 comprises a core 4 a having a short predeterminedlength. In this embodiment, the length of the core 4 a is less than onehalf of the length of the sensor coil 2 comprising the first sensor coil2 a and the second sensor coil 2 b. The core support 3 connects the core4 a with the piston so that the core 4 a can move according to thereciprocal movement of the piston.

As the core 4 a combined to the piston of the compressor reciprocallymoves back and forth along an inner hole of the bobbin 1, apredetermined reactance is generated in the sensor coil 2 according tothe reciprocal movement of the core 4 a within the sensor coil 2.

The core 4 a moves reciprocally, centering around the first sensor coil2 a through a complete cycle of the piston. Further the core 4 a isadjusted to reach near the second sensor coil 2 b through a middle pointbetween the first sensor coil 2 a and the second sensor coil 2 b (willbe referred as a coil origin) when the piston arrives in a top deadcenter. Also, the size of the bobbin and the piston should be preferablyconfigured so that the core 4 a can come out of the bobbin 1 during anexpansion stroke. Alternatively, this cycle may be reversed so that thecore 4 a exits the bobbin 1 during an inhale stroke.

If the state of the load on the linear compressor turns into anoverloaded state, a stroke of the piston comes out of the bobbin 1 in anexpansion stroke.

Such change of the state of the load can be determined by measuring timetaken for the center point of the core 4 a to exit and enter the bobbin1.

A controller 13 as shown in FIG. 5, measures the time that the core 4 atakes to exit and enter the bobbin 1 to determine the state of the load.In a case of overload, the controller 13 applies a high current to adriving motor of the linear compressor.

However, in case of an extreme overload, the top clearance of the pistonmay be increased by a partial amount of the load calculated andcontrolled by the controller when the change of the measured load isgreater than a predetermined critical amount of the load. A reason forincreasing the top clearance is that the overcontrolled piston maycollide with a valve of the linear compressor if the state of theoverload turns into the state of a steady load abruptly as the magnitudeof the stroke of the piston during the overload increases. Accordingly,it is beneficial to prevent an abnormal operation of the piston bysetting the top clearance of the piston to a value that is adequate overa broad load range.

The position of the piston may be controlled by determining the state ofthe load by measuring the time that the core 4 a takes to exit and enterthe bobbin 1. Hereinbelow, a method to measure the time that the core 4a takes to exit and enter the bobbin 1 will be described. FIG. 5 is ablock diagram of a position detection circuit for the piston of thelinear compressor according to the embodiment of the present invention.

As illustrated in FIG. 5, the position detection circuit comprises afirst sensor coil 2 a, a second sensor coil 2 b, a first dividingresistor R1, a second dividing resistor R2, a power source 10, a voltagecomparator 11, a digital signal processor 12, and a controller 13.

The power source 10 applies power to a first branch having the firstsensor coil 2 a and the first dividing resistor R1 connected in series,and to a second branch having the second sensor coil 2 b and the seconddividing resistor R2 connected in series.

The voltage comparator 11 receives voltages taken from a terminal ofeach of the first dividing resistor R1 and the second dividing resistorR2 as a comparison signal V+ and a comparison signal V−, respectively.Also, the voltage comparator 11 may receive voltage taken from theopposite terminals of each of the first sensor coil 2 a and the secondsensor coil 2 b.

The digital signal processor 12 transmits a rectangular pulse to thecontroller 13 according to an output of the voltage comparator 11, andthen the controller 13 controls a driving motor (not shown) of thelinear compressor on the basis of the rectangular pulse.

FIGS. 6A through 6C and 7A through 7C are input waveforms of a voltagecomparator according to reciprocal movement of the piston of the linearcompressor.

FIG. 6A represents a triangle pulse from the power source 10, and FIG.6B represents waveforms input to a positive terminal and a negativeterminal of the voltage comparator 11.

FIG. 6B represents the input waveform of the voltage comparator 11 whena center point of the upper core 4 a (will be referred to as a coreorigin) passes a middle point between the first sensor coil 2 a and thesecond sensor coil 2 b (will be referred to as a coil origin), or whenthe piston reaches near a top dead center by a compression stroke. Ifthe triangle pulse is applied from the power source 10, an inductance L2of the second sensor coil 2 b becomes greater than an inductance L1 ofthe first sensor coil 2 a. Accordingly, the input waveform V− input intothe negative terminal of the voltage comparator 11 has a time delaylonger than the time delay of the input waveform V+ input into thepositive terminal of the voltage comparator 11.

As illustrated in FIG. 6C, the digital signal processor 12 generates arectangular waveform Vd having high level when the input waveform V+ ofthe positive terminal of the voltage comparator 11 is greater than theinput waveform V− of the negative terminal.

FIGS. 7A through 7C are waveforms when the core origin is inclinedtoward the first sensor coil 2 a from the coil origin. In this case, theinductance L1 of the first sensor coil 2 a becomes greater than theinductance L2 of the second sensor coil 2 b. Accordingly, the inputwaveform V+ input into the positive terminal of the voltage comparator11 has a longer time delay. FIG. 7B illustrates input waveforms of thevoltage comparator 11 in such case, and FIG. 7C illustrates arectangular waveform Vd outputted from the digital signal processor 12corresponding to the waveforms in FIG. 7B.

FIG. 9 is a waveform output from the voltage comparator 11 according toa position of the piston of the linear compressor according to thisembodiment of the present invention.

As illustrated in FIG. 9, a waveform “c” has two zero pointscorresponding to the input waveforms illustrated in FIGS. 6B and 7B.

If the core origin of the core 4 a passes the coil origin, the outputwaveform V₀ of the voltage comparator 11 has a second zero point, and ithas a first zero point if the core origin of the core 4 a comes out ofthe bobbin 1.

FIG. 8 is a control block diagram of the linear compressor according toan embodiment of the present invention. Hereinbelow, the embodiment ofthe present invention will be described in reference to FIGS. 4 through8.

At operation S1, the time for the core origin of the core 4 a to exitand enter the bobbin 1 according to an inhale stroke of the piston ismeasured, or the time that is taken for the output V₀ of the voltagecomparator 11 having the first zero point to have the first zero pointagain according to the compression stroke is measured. Then, atoperation S2, the state of the load on the piston can be determinedbased on the measured result.

In operation S4, the controller 13 checks the trend of the load. If theload decreased, the controller 13 will control the stroke of the pistonto decrease accordingly in operation S3, however, if the state of theload is determined to be the overload, it is decided whether the amountof the change of the load is greater than the amount of thepredetermined critical load at operation S4 then the controller mustadjust the top clearance of the piston in operation S5.

The controller 13 increases the driving current for the driving motor toincrease the stroke of the piston if the state of the load is determinedto be the overload at operation S6. However, the piston may collide withthe valve as the piston becomes uncontrollable with a big stroke becausethe driving current for the driving motor increases when the increasedamount of the load is greater than the amount of the critical load, orbecause a controlled velocity of the motor becomes lower than a changingvelocity of the load when the state of the load turns into the steadystate suddenly.

Accordingly, when the magnitude of the change of the load is great, itis desirable to change the magnitude of the stroke slowly by setting atarget magnitude of the controlled stroke greater than the presentmagnitude of the stroke by some amount rather than to change themagnitude of the stroke of the piston abruptly by increasing the drivingcurrent for the driving motor. However, the collision of the piston andthe valve may be prevented by increasing the top clearance by adjustingthe target magnitude of the controlled stroke at operation S5.

The linear compressor according to this embodiment of the presentinvention detects the amount of the load and controls the cooling powerbased on the detected amount of the load.

Waveforms “c” and “d” in FIG. 9 are the output waveforms V₀ of thevoltage comparator 11 when the external environmental conditions of thesensor such as the temperature and the pressure change. The waveform “d”illustrates that the zero point does not vary even if the externalconditions changed compared to the waveform “c”. Accordingly, it can beinferred that the external environment does not affect the zero points,which enables accurate determining the state of the load and controllingthe position of the piston based on the zero points.

This embodiment provides the present invention a control of high qualityon the stroke of the piston by determining the state of the loadregardless of the external environment.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A linear compressor having a core combined to one end of a piston todetect a position of the piston reciprocally moving up and down, and abobbin having a first sensor coil and a second sensor coil detecting theposition of the core, comprising: a controller determining a state of aload of the piston by measuring time that the core takes to exit andenter the bobbin from an inhale stroke through a compression stroke ofthe piston and controlling a position of the piston on a basis of thedetermined state of the load.
 2. The linear compressor according toclaim 1, wherein the core has a length shorter than one half of thelength of the first sensor coil and the second sensor coil in series. 3.The linear compressor according to claim 1, wherein the controllerincreases a top clearance of the piston if the time that the core takesto exit and enter the bobbin increases over a predetermined criticaltime.
 4. The linear compressor according to claim 1, further comprising:a first branch comprising the first sensor coil and a predeterminedfirst dividing resistor connected in series; a second branch comprisingthe second sensor coil and a predetermined second dividing resistorconnected in series; a power source applied to the first branch and thesecond branch; and a voltage comparator with input voltages applied fromthe first dividing resistor and the second dividing resistor.
 5. Thelinear compressor according to claim 4, wherein the voltage comparatorreceives input voltages applied from the terminals of each of the firstsensor coil and the second sensor coil.
 6. The linear compressoraccording to claim 4, wherein the controller determines the state of theload on the piston based on the time that the piston takes to bepositioned near the bottom dead center making output of the voltagecomparator 0, so as to control the position of the piston.
 7. The linearcompressor according to claim 5, wherein the controller determines thestate of the load on the piston on a basis of difference of time thatthe piston takes to be positioned near the bottom dead center makingoutput of the voltage comparator 0, so as to control the position of thepiston.
 8. A control method of a linear compressor having a corecombined to one end of a piston to detect a position of the pistonreciprocally moving up and down, and a bobbin having a first sensor coiland a second sensor coil detecting the position of the core, comprising:measuring a time that the core takes to exit and enter the bobbin froman inhale stroke through a compression stroke of the piston; andcontrolling a position of the piston by determining state of a load onthe piston on a basis of the time that the core takes to exit and enterthe bobbin.
 9. The control method of the linear compressor according toclaim 8, further comprising forming a length of the core to be shorterthan a half of length of the first sensor coil and the second sensorcoil connected in series.
 10. The control method of the linearcompressor according to claim 8, further comprising increasing a topclearance of the piston if the time that the core takes to exit andenter the bobbin increases above a predetermined critical time.
 11. Amethod for controlling an operation of a linear compressor, comprising:timing a core driven by a piston through a stroke cycle; receiving thetime and computing a load on the piston; outputting a piston positionsignal based on the load computed; and controlling a piston strokeaccording to the piston position signal, by varying the power drivingthe linear compressor.
 12. The method of claim 11, wherein thecontrolling further comprises controlling the piston stroke, wherein thepiston stroke is increased as the load increases and the piston strokeis decreased as the load decreases.
 13. The method of claim 11, whereinthe controlling further comprises if the load computed is greater than apredetermined critical load amount, then increasing a top clearance ofthe piston.
 14. The method of claim 11, wherein timing the core is basedon the elapsed time when the core exits the sensor coil aperture duringa compression stroke, and then enters the sensor coil aperture during aninhale stroke of the piston.
 15. The method of claim 11, wherein timingthe core is based on the elapsed time when the core enters the sensorcoil aperture during a compression stroke, and then exits the sensorcoil aperture during an inhale stroke of the piston.
 16. A linearcompressor piston control device, comprising: a bobbin defining anaperture; a sensor coil disposed in the bobbin; a core attached to apiston disposed coaxially in the aperture of the bobbin, wherein thecore is less than one half the length of the sensor coil; a controllercontrolling a position of the piston by determining a load based onsignals from the sensor coil sensing the position of the core.
 17. Thecontrol device according to claim 16, wherein the controller determinesthe load based on the elapsed time when the core exits the sensor coilaperture during a compression stroke and then enters the sensor coilaperture during an inhale stroke of the piston.
 18. The control deviceaccording to claim 17, further comprising the controller adjusting a topclearance of the piston based on the elapsed time.
 19. The controldevice according to claim 18, wherein the controller increases the topclearance if the elapsed time is above a predetermined critical time.20. The control device according to claim 16, wherein the sensor coilincludes a first sensor coil and a second sensor coil.
 21. The controldevice according to claim 20, wherein the first sensor coil and thesecond sensor coil have the same number of turns, size and inductancevalue.
 22. The control device according to claim 21, wherein the controldevice further comprises: a first branch having a first predetermineddividing resistor connected in series with the first sensor coil; asecond branch having a second predetermined dividing resistor connectedin series with the second sensor coil.
 23. The control device accordingto claim 22, further comprising: a voltage comparator that receivesvoltage inputs from the first branch and the second branch and outputs acomparator signal; a digital signal processor that receives thecomparator signal and sends an output signal to the controller based onthe comparator signal.
 24. The control device according to claim 23,wherein the controller determines the load by measuring the time thatelapses between the comparator signal equaling 0 a first time during acompression stroke and the comparator signal equaling 0 a second timeduring an inhale stroke.